This invention relates to fluid control devices, in particular valves, which are actuated by partial-revolution DC motors. More particularly, the invention relates to devices of the aforestated type which are electronically controlled to provide a modulating valve for regulating fluid conditions. Specifically, the invention relates to devices of the aforestated type utilizing a brushless DC motor in which the rotor is axially movable to directly carry the valve poppet, thereby providing a single stage fluid control device.
Fluid control devices of the type to which this invention is related employ a modulating valve to regulate fluids. Such devices may be used as shut-off valves, pressure regulators, mass flow rate regulators, volumetric flow rate regulators or pressure relief valves for fluids in liquid or gaseous form. The fluids may be corrosive and/or flammable in nature and therefore the fluid contacting portions of the valve structure must be corrosion resistant and must not provide an ignition source. It is preferable that such devices avoid small flow passages which are susceptible to clogging. Electronic controllers are employed which respond to command and feedback signals sensed by transducers to control a partial-revolution DC motor to regulate the valve opening. Present fluid control devices of this type are two stage devices wherein electrical energization of the motor operates a small pilot valve which in turn operates the main valve. The fluid passage for the pilot valve is considerably smaller than the main fluid passage and is susceptible to clogging. Additionally, the small pilot valve adds complexity to the design and requires dynamic seals. Moreover, the motor must be sealed from contact with the fluid and motion transmitting bellows are often employed for this purpose. The pilot valve two stage device often employs a main-stage bellows for operating the main valve, such bellows being sensitive to cycling and pressure levels.
This invention provides a fluid control device having several advantages over the presently available two stage systems. The fluid control device of this invention is a single stage device utilizing a two pole brushless DC motor wherein the rotor is mounted for rotational and axial movement within a cylindrical chamber of the housing by bearings projecting from the periphery of the rotor and slidingly engaging the interior surface of the valve chamber. The rotor integrally carries the poppet, thereby providing only a single moving unit within the device. With no electrical power applied, magnetic flux of permanent magnets of the rotor react with ferromagnetic material of the stator core to axially position the rotor and poppet in the valve closed position. By utilizing a brushless DC motor, contamination and potential for explosion due to electrical arcs from motor brushes are eliminated, and thus the rotor may be exposed to the fluid. The two pole brushless DC motor significantly simplifies the device by eliminating the need to commutate the stator windings, therefore also eliminating transducers such as Hall effect devices and associated circuitry to perform such commutation. Two embodiments of valve opening mechanisms are disclosed which may be constructed to provide variable "lift per revolution", or "lead". The electronic control employs a pulse width modulation driver to minimize self-heating in the motor and controller and to provide fast efficient response to varying conditions sensed by transducers, which may be integrally mounted within the device or mounted within the system.